The invention relates to two stroke engines, and more particularly to those with two or more spark plugs per combustion chamber.
Two stroke engines in general exhibit poor idling, and are subject to numerous misfires. This causes rough and noisy running at idle, higher hydrocarbon emissions, and higher idle fuel consumption. In the present invention, it has been found that a particular type of positioning of dual spark plugs in the combustion chamber produces a misfire-free idle in loop-scavenged two stroke engines, including direct injection, i.e. cylinder head injection, and intake manifold injection or carburetion.
Two stroke engines with dual spark plugs are known in the art, for example as shown in U.S. Pat. No. 4,538,568. In this patent, torque is maximized when the ratio d/D is in the range of about 0.35 to 0.45, where d is the distance between the two ignition plugs, and D is the inner diameter of the cylinder.
In the present invention, it has been found that a different ratio d/D is needed to produce misfire-free idle. Furthermore, it has been found that a particular height ratio h/H is desired to produce misfire-free idle, where h is the height of the spark gaps above the squish surface, or top of the cylindrical sidewall, and H is the height of the combustion chamber above such surface. It has been found that the ratio h/H should be less than about 0.5.